High-Resolution Differential Thermocouple Measurements Using an Improved Noise Cancellation and Magnetic Amplification Technique
K. C. Sloneker · AIP conference proceedings · 2003
Comparing two absolute temperature measurements using thermistors, RTDs, or thermocouples has proven to be the best method of obtaining differential measurements. In spite of their susceptibility to external influences and physical changes during use, thermocouples are well suited for making direct differential measurements over a wide range of temperatures and hostile environments. To improve differential temperature measurements will mean improvements in other parameters such as pressure and flow, as they are fundamentally dependent on temperature. This paper describes a novel method of making differential thermocouple measurements. Under the control of a digital timing circuit, a discrete quantity of energy is magnetically amplified. A null‐balancing method is used to quantify the signal and develop its relationship to temperature. Since the balancing method utilizes a current flow within the system, the Peltier effect at the junctions of the differential thermocouple is discussed. Common mode noise is effectively cancelled by a physical balancing method that is part of a negative feedback system. Reduction of variances caused by changing magnetic fields is accomplished by using an optically isolated timing system that is synchronized to local power. The equations describing the operation of the device are presented in the form of a set of differential equations. Measurements have been made at 0 °C to a resolution of 1 mK. The system can resolve to the 0.1 mK level, but testing is difficult because of limitations in our laboratory establishing this low differential temperature. With further development, the described method could be applied to improving many types of measurements, for example, low‐level pressure measurements, and possibly high accuracy absolute measurements. The method described follows a different path for its solutions; they are not found by using traditional digital electronics, but use a more unique method of amplification and measurement.